title: Abscisic acid coordinates nod factor and cytokinin signaling during the regulation of nodulation in Medicago truncatula.
abstract: Nodulation is tightly regulated in legumes to ensure appropriate levels of nitrogen fixation without excessive depletion of carbon reserves. This balance is maintained by intimately linking nodulation and its regulation with plant hormones. It has previously been shown that ethylene and jasmonic acid (JA) are able to regulate nodulation and Nod factor signal transduction. Here, we characterize the nature of abscisic acid (ABA) regulation of nodulation. We show that application of ABA inhibits nodulation, bacterial infection, and nodulin gene expression in Medicago truncatula. ABA acts in a similar manner as JA and ethylene, regulating Nod factor signaling and affecting the nature of Nod factor-induced calcium spiking. However, this action is independent of the ethylene signal transduction pathway. We show that genetic inhibition of ABA signaling through the use of a dominant-negative allele of ABSCISIC ACID INSENSITIVE1 leads to a hypernodulation phenotype. In addition, we characterize a novel locus of M. truncatula, SENSITIVITY TO ABA, that dictates the sensitivity of the plant to ABA and, as such, impacts the regulation of nodulation. We show that ABA can suppress Nod factor signal transduction in the epidermis and can regulate cytokinin induction of the nodule primordium in the root cortex. Therefore, ABA is capable of coordinately regulating the diverse developmental pathways associated with nodule formation and can intimately dictate the nature of the plants' response to the symbiotic bacteria.
authors.affiliation: Department of Disease and Stress Biology, John Ines Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom.
authors.forename: Yiliang
authors.initials: Y
authors.lastname: Ding
authors.forename: Peter
authors.initials: P
authors.lastname: Kalo
authors.forename: Craig
authors.initials: C
authors.lastname: Yendrek
authors.forename: Jongho
authors.initials: J
authors.lastname: Sun
authors.forename: Yan
authors.initials: Y
authors.lastname: Liang
authors.forename: John F
authors.initials: JF
authors.lastname: Marsh
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Harris
authors.forename: Giles E D
authors.initials: GE
authors.lastname: Oldroyd
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology*; D003583:Cytokinins / Q000378:metabolism*; D005030:Ethylenes / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D046913:Medicago truncatula / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D008969:Molecular Sequence Data; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D055170:Plant Root Nodulation / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects*; D016962:Sinorhizobium meliloti / Q000502:physiology
chemical_list: D003583:Cytokinins; D005030:Ethylenes; D010937:Plant Growth Regulators; D010940:Plant Proteins; D000040:Abscisic Acid; C036216:ethylene